In recent years there has developed an increased incidence of cervical intraepithelial neoplasia (CIN), i.e., sexually transmitted genital warts. Since the majority of cases occur in women of reproductive age who have not completed their families, conservative treatment has been advisable.
Management procedures using electrocoagulation, electrodiathermy, cryosurgery and laser surgery are accepted but each such procedure has drawbacks and all require considerable skill and experience. Cold knife and laser surgery typically require hospitalization and general anesthesia. Using these procedures, there are occasions when the practitioner will miss invasive cancers or inadvertently treat cancers with ablative therapy.
Recently, loop electrosurgical excision procedures (LEEP) and large loop excision of the transformation zone (LLETZ) using thin wire electrodes have been used to treat CIN. These electrosurgical techniques can be provided on an outpatient basis under either local or general anesthesia. Also, these electrosurgical techniques have the advantage over other destructive techniques in that the specimen excised is not destroyed, but preserved for examination histologically. Additionally, microinvasive and invasive disease can be excluded and the limits of the lesion are clearly defined.
In performing these electrosurgical techniques, the loop is used with a monopolar generator (the "electrosurgical unit") which produces a number of waveforms for electrosurgical cutting and coagulation. In monopolar electrosurgery, a radio frequency current is passed through the body of the patient between an active electrode, where the current is very concentrated, and a disperse electrode, where the current is quite diffuse. The loop acts as the active electrode and is used as a cutting tool at the surgical site. The loop comprises an insulated shaft connected to insulated extending arms to which a loop wire is attached. The loop is connected to and is controlled by either a hand switch or a foot switch connected to the electrosurgical unit. The dispersive electrode is applied to the patient's body at a site away from the surgical field. Its purpose is to complete the electrical circuit and disperse the current returning to the electrosurgical unit.
Electrosurgery results from the concentration of electrical energy in tissue of the patient to the point that local tissue is destroyed or modified. In electrosurgical cutting, the cells conducting the concentrated current are heated to where the water contained within the cells boils causing the cells to explode and release the resulting steam. In electrosurgical coagulation, cells near the surface exposed to the concentrated current are heated so that they dehydrate and shrink, rather than explode, thereby closing open vessels.
To obtain cutting with a minimal heating, the electrosurgical unit drives the mall-wire loop with a continuous, unmodulated waveform. Cutting with shallow surface coagulation is obtained by modulating the cutting power source. This is known as a blended source. Typical electrosurgical units have a pure cut mode and multiple (usually three) blend modes. These blend modes use waveforms comprising bursts of radio frequency energy with smaller duty cycles causing greater coagulation activity and less cutting activity.
To obtain coagulation without cutting, typically an active electrode with larger cross section is used with the power source supplying an interrupted waveform. Two forms of coagulation are desiccation and fulguration. Desiccation coagulation is accomplished using a blunt active electrode, a coag or high blend waveform, and relatively low power. The less concentrated current dries and shrinks the affected cells causing a deeper penetration of thermal modification to the cells than is accomplished using a blend mode during cutting or by fulguration. Fulguration coagulation is accomplished using either a blunt or fine electrode with a coag mode waveform at high power. The active electrode is kept slightly spaced from the surface to be coagulated so that sparks jump across the gap. The surface area contacted by and the current from each spark is small so that the resulting thermal modification is shallow.
To avoid electrical shock to the patient caused by the depolarization of nerve or muscle cells by a non-physiologic electric voltage, frequencies above 300 kHz are used. To avoid electrical burns, the dispersive electrode must be carefully applied and care must be taken that the patient avoid metallic contacts. Further, the surgeon handling the active electrode must avoid applying it to his or her own body or touching it to any conductive tool or appliance.
Typically, a patient with an abnormal smear obtained during a colposcopic examination is identified as a candidate for an electrosurgical excision procedure using a loop. At the beginning of the procedure, routine colposcopy is performed using acetic acid and iodine to outline the cervical lesion. The patient is anesthetized and the dispersive electrode is applied.
After the patient has been prepared as briefly set forth above, the hand or foot control is activated thereby activating the loop. Using a slight downward pressure, the loop is pushed into the cervical tissue perpendicular to the surface as deeply as needed, but not too deeply. The loop is then advanced slowly across the cervix underneath the transformation zone and then withdrawn perpendicular to the surface of the cervix. The entire excision takes only about 5 to 10 seconds. The excised specimen is then removed for examination. After the excision, a diathermy ball operated at the coagulation mode is used to coagulate the cervical wound.
Electrosurgical excisions using a loop have several advantages over other procedures using a laser, cold knife, or cryogenic techniques. The tissue is removed rather than destroyed so that the entire transformation zone may be sent for histological examination. This minimizes the possibility of missing invasive disease. Additionally, the procedure may be performed at a patient's first visit to a colposcopy clinic, thereby affording valuable time savings to the patient and the colposcopy clinic.
Although the procedure for electrosurgical excision using a loop which has been described briefly above has marked advantages, there is a serious precaution that must be followed during the procedure. Precaution must be taken not to cut too deeply into the cervix. A range of depths from 5 to 8 mm is the preferred depth for the cut. Despite the inherent dangers of cutting too deeply and the speed with which the loop cuts readily through tissue, the depth of the cut has heretofore been left to the skill and experience of the surgeon. However, as the procedure becomes more widely known and practiced, surgeons having less experience with the technique are using it on their patients.
Hence, it would be a substantial contribution to electrosurgical excision using a loop if an improved apparatus and method for gauging the depth of the cut could be provided. It would be a further advance in the art if the apparatus could be used on a loop that optimizes the ability of the surgeon to visually observe the cut. The present invention provides such an apparatus and method.